This invention relates to a cathode ray tube comprising a display screen and an electron gun having a means for generating electrons, a number of electrodes and a support which is composed of an insulating material, said electrodes being provided with connecting elements which are secured in the support.
Cathode ray tubes are used, inter alia, in television receivers, computer monitors, oscilloscopes etc.
A cathode ray tube of the class mentioned in the opening paragraph is of the conventional type. The electron gun comprises a means for generating electrons, for example, a cathode. The electrodes are provided with connecting elements which are pressed into the support. The support is generally made from glass which can be softened. In the manufacture of the electron gun, the electrodes of the electron gun are stacked on top of each other, whereafter the support is (or are, if more than one support is used) heated. By virtue thereof, the support and the projections can be interconnected. This is generally achieved by pressing the support against the projections. Since the glass has been softened by heating, the connecting elements can be inserted into the support. The connecting elements may be integral with the electrode or they may be secured to the electrode as a separate part. After cooling, the electrodes and the support are secured to each other.
In operation, voltages are applied to the electrodes. Due to said voltages, electro-optical fields are formed between the electrodes. The electrons generated are accelerated and focused by means of said electric fields. Ever higher demands are imposed on the quality of the electron-optical fields. As a result thereof, the number of electrodes in the electron gun and the value of the applied voltages increase. A problem which arises is that sometimes the electrodes themselves can generate electrons. These electrons may hop between the electrodes. Due to this, the cathode ray tube may be damaged, which leads to failure. Such electrons may also land on the display screen, thereby adversely affecting the contrast of the image displayed. These phenomena occur, in particular, at locations where high voltages are applied to the electrodes.
It is an object of the invention to provide a cathode ray tube of the type mentioned in the opening paragraph, in which one or more than one of the above problems is reduced.
To this end, the cathode ray tube in accordance with the invention is characterized in that the electron gun comprises a pair of electrodes which are arranged one behind the other, said electrodes having connecting elements extending in a plane transverse to the electron beam, the width of the connecting elements of one of the electrodes of the pair of electrodes differing from the width of the connecting elements of the other electrode of the pair of electrodes.
Hopping of electrons between two electrodes can be reduced by varying the width of the connecting elements. In well-known electron guns, the connecting elements of successive electrodes are equal width.
The invention is, inter alia, based on the insight that electrons can readily hop from one electrode to a proximate electrode via a connecting element and to a connecting element of a nearby electrode via the support, and that in this process the edges the connecting elements form an important source of electrons. By making the widths of the connecting different elements, the shortest distance, via the support, between the edge of connecting element of one electrode, and the next electrode is increased.
In a preferred embodiment, the cathode ray tube comprises means for applying voltages to the pair of electrodes, and the voltage applied to the electrode having the widest connecting elements is lower than the voltage applied to the electrode having the narrowest connecting elements.
In particular in this embodiment hopping of electrons is reduced.